In a burner which burns a pulverized coal in a furnace of a boiler, there is a burner, for performing oxyfiring, which makes the greater part of recirculated flue gas become a carbon dioxide and makes it easy to capture carbon dioxide, by using a mixed a gas of recirculated flue gas and oxygen as a carrying medium to carry a pulverized coal and likewise by using the mixed gas of recirculated flue as and oxygen as a combustion air.
Further, since there is a possibility that in a case where the mixed gas of recirculated flue gas and oxygen is used as the carrying medium, the oxygen concentration in the carrying medium increases due to an emergency stop or the like of an apparatus and the pulverized coal ignites during carriage, a burner such that does not mix oxygen into a carrying medium and only uses recirculated flue gas as the carrying medium has also been devised.
However, in a case where only the recirculated flue gas is used as the carrying medium without mixing the oxygen into the recirculated flue gas, since the oxygen concentration in the recirculated flue gas is as low as approximately 3% to 5%, the oxygen is not sufficiently supplied to a pulverized coal mixed flow even if the combustion air is supplied from the periphery at the time of the combustion, and thus, a problem may arise that the ignition becomes unstable.
It is to be noted that Patent Document 1 discloses an oxyfuel boiler plant which spurts out a primary gas, which is a mixture of pulverized coal and recirculated flue gas, from the center of the burner into a furnace, supplies a secondary gas from a periphery of the primary gas, supplies a tertiary gas provided by dividing the secondary gas from a periphery of the secondary gas, and has an oxygen-enriched gas spurt nozzle that spurts out an oxygen-enriched gas installed in the primary system piping on the burner upstream side.